#include <regex>
#include <string>
#include <iostream>
using namespace std;

int main() {
    std::regex matchPattern(R"(@([^=]+))");
    std::string s("@test=boundary");
    std::smatch matches;
    if (std::regex_search(s, matches, matchPattern)) {
        std::cout<<matches.str(1);
    }
    return 0;
}